Image forming system

ABSTRACT

An image forming system includes an image forming apparatus that that forms an image on a paper sheet and a sheet finishing device that performs finishing on a paper sheet discharged from the image forming apparatus. The sheet finishing device is disposed beneath the image forming apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2009-202468 filedin Japan on Sep. 2, 2009 and Japanese Patent Application No. 2009-051877filed in Japan on Mar. 5, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet finishing device that isdisposed integrally or separately with respect to an image formingapparatus such as a copying machine, a printer, or a printing machineand that performs predetermined finishing processing on a paper sheethaving an image formed thereon, and relates to an image forming systemthat includes the sheet finishing device and the image formingapparatus.

2. Description of the Related Art

Sheet finishing devices are known in art that are disposed integrally orseparately with respect to an image forming apparatus such as a copyingmachine, a printer, or a printing machine. The sheet finishing deviceperforms predetermined finishing processing such as stacking, aligning,stapling, saddle stitching, and folding with respect to a paper sheet(recording medium) having an image formed thereon in the image formingapparatus (see Japanese Patent No. 3940008, Japanese Patent ApplicationLaid-open No. 2007-161468, and Japanese Patent No. 3973973).

An image forming system is built by assembling a sheet finishing devicewith an image forming apparatus (main body).

Typically, it is common practice to dispose a sheet finishing devicelaterally with respect to the main body of the image forming apparatus.Such a configuration leads to an increase in the total occupancy area ofthe image forming system. In particular, the occupancy area of the imageforming system increases when a sheet finishing device having a saddlestitching mode and a variety of folding modes is installed.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention there is provided animage forming system including an image forming apparatus that forms animage on a paper sheet; and a sheet finishing device that performsfinishing of a paper sheet discharged from the image forming apparatus.The sheet finishing device includes an aligning unit that stacks andaligns a plurality of paper sheets on an alignment tray thereby forminga sheet stack, and a stapling processing unit that performs staplingwith respect to the sheet stack. The sheet finishing device is disposedbeneath the image forming apparatus.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram for explaining an overall configurationof an image forming system according to a first embodiment of thepresent invention;

FIG. 2 is an explanatory diagram for explaining an overall configurationof an image forming system according to a second embodiment of thepresent invention;

FIG. 3 is an explanatory diagram for explaining an overall configurationof an image forming system according to a third embodiment of thepresent invention; and

FIG. 4 is an explanatory diagram for explaining an overall configurationof an image forming system according to a fourth embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detailbelow with reference to the accompanying drawings. The present inventionis not limited to these exemplary embodiments.

FIG. 1 is a front longitudinal sectional view of an overallconfiguration of an image forming system including a sheet finishingdevice according to a first embodiment of the present invention.

The image forming system includes a sheet finishing device 1 and animage forming apparatus 100. The image forming apparatus 100 can be acopying machine, a printer, a printing machine etc.

In the image forming apparatus 100, tasks such as setting paper sheetsinside the apparatus (setting paper sheets by pulling out a sheet feedtray) or replacing/refilling consumable components is performed byopening and closing a door 101 disposed on the front surface (right sidein FIG. 1). The image forming apparatus 100 includes a sheet feed tray105, an image forming unit 106, an optical writing unit 107, and a sheetdischarging path 108.

The sheet finishing device 1 is disposed beneath the image formingapparatus 100 and includes a feed inlet 2 and an entry roller pair 3though which enters a paper sheet P that is discharged from adischarging outlet 103 at the lower back portion of the image formingapparatus 100; an aligning unit 10 that is disposed on the downstreamside of a feed path 4 and that sequentially discharges and stacks papersheets as a sheet stack on an alignment tray 11; a stapling processingunit 20 that performs edge stapling or saddle stitching on the sheetstack and discharges the stapled sheet stack in the anterior directionof the apparatus (right direction in FIG. 1); a folding processing unit(center folding processing unit) 30 that performs center folding on thesheet stack that has been stapled (edge-stapled or saddle-stitched) bythe stapling processing unit 20; and a control unit (not illustrated)that controls the abovementioned operations. Meanwhile, the centerfolding processing unit performs center folding at the central part ofthe sheet stack along the sheet conveying direction.

The aligning unit 10 aligns the paper sheets in the conveying directionand the width direction (perpendicular direction to the conveyingdirection). The stapling processing unit 20 includes an edge staplingunit (not illustrated) that staples an edge of the sheet stack and asaddle stitching unit (not illustrated) that staples the central part ofthe sheet stack. Moreover, at the topside of the stapling processingunit 20 is disposed a driver unit 21 that includes a stapler pincontainer (not illustrated) and a stapler pin pushing unit (notillustrated); while at the lower side of the stapling processing unit 20is disposed a clincher unit 22 used in folding the ends of stapler pins.

An edge-stapled sheet stack that has been edge-stapled by the staplingprocessing unit 20 is placed on an edge-stapled-stack tray (firstdischarging tray) 25, while a center-folded sheet stack that is foldedin center after being saddle-stitched by the stapling processing unit 20is placed on a center-folded-stack tray (second discharging tray) 26.The trays 25 and 26 have independent configurations. More particularly,the edge-stapled-stack tray 25 is disposed on the downstream side (rightside) of the stapling processing unit 20 and the center-folded-stacktray 26 is disposed on the upper side of the edge-stapled-stack tray 25.

The folding processing unit 30 is a center folding processing unit thatis disposed on the upstream side of the stapling processing unit 20 andthat performs center folding of a stapled sheet stack. When centerfolding is to be performed, a saddle-stitched sheet stack isreversely-conveyed from the stapling processing unit 20 to the centerfolding processing unit.

The sheet finishing device 1 is disposed beneath the image formingapparatus 100 and a recording medium (paper sheet) discharged from thelower back portion of the image forming apparatus 100 is guided into thesheet finishing device 1. The entry roller pair 3 then conveys the papersheet on the alignment tray 11. The paper sheet gets aligned on thealignment tray 11 in the direction (width direction) perpendicular tothe sheet conveying direction by a jogger fence 12 disposed on the nearside as well as the rear side. The alignment in the sheet conveyingdirection is performed by a return roller 13 with reference to a rearend fence 14.

Once the sheet stack is aligned in the sheet conveying direction and thewidth direction on the alignment tray 11, a movable sheet-stackconveying roller 40 disposed on the upper side moves toward a fixedsheet-stack conveying roller 41 disposed on the lower side so that thesheet stack is nipped therebetween and conveyed to the staplingprocessing unit 20 disposed on the downstream side. The movablesheet-stack conveying roller 40 and the fixed sheet-stack conveyingroller 41 are driving rollers that are driven by a driving force of amotor (not illustrated) and that enhance the conveyance quality (sheetfeed precision/positional accuracy of sheet stack). The movablesheet-stack conveying roller 40 can move up and down with respect to thefixed sheet-stack conveying roller 41 and is configured to form a nipwith the fixed sheet-stack conveying roller 41. Thus, when a paper sheetpasses through the nip position between the rollers 40 and 41, aconveying force is exerted on the paper sheet.

In the case of edge stapling performed by the stapling processing unit20, the sheet stack is conveyed to the downstream side after thestapling is performed at a predetermined position. Then, the sheet stackis conveyed and stacked on the edge-stapled-stack tray 25 by a pair ofedge stapling discharging rollers 45.

In the case of saddle stitching performed by the stapling processingunit 20; after the sheet stack is aligned, the movable sheet-stackconveying roller 40 moves toward the fixed sheet-stack conveying roller41 so that the sheet stack is nipped therebetween and conveyed to thestapling processing unit 20 on the downstream side. Then, the staplingprocessing unit 20 performs stapling at a saddle stitching position.Upon completion of saddle stitching, the sheet stack isreversely-conveyed by the sheet-stack conveying rollers 40 and 41 to afolding position on the upstream side. At the folding position in thefolding processing unit 30, a folding plate 31 and a pair of foldingrollers 32 perform center folding of the sheet stack. Then, a pair ofcenter-folded-sheet discharging rollers 33 discharges and stacks thecenter-folded sheet stack on the center-folded-stack tray 26. Moreparticularly, the folding plate 31 is configured to move up and down atthe folding position and moves toward a space between the pair offolding rollers 32, which are juxtaposed over the top surface of thesheet stack, so that the intermediary position of the sheet stack getsfolded.

In this way, according to the first embodiment, it is possible toarrange the sheet finishing device 1 beneath the image forming apparatus100 thereby reducing the installation area. As a result, the imageforming system can be installed in a smaller place.

Moreover, since the edge-stapled-stack tray 25 and thecenter-folded-stack tray 26 have independent configurations and sincethe center-folded-stack tray 26 is disposed above the edge-stapled-stacktray 25, sheet stacks having different stapled conditions or foldedconditions can be prevented from getting mixed and the occupancy area ofthe apparatus can be prevented from increasing.

Furthermore, since the folding processing unit 30 (folding plate 31,pair of folding rollers 32, etc.) is disposed on the upstream side ofthe stapling processing unit 20, the folding processing is performedrearward than the intermediary position in the longitudinal direction ofthe sheet finishing device 1. For that reason, it becomes possible toincrease the space anterior to the folding processing unit 30 and usethat space to dispose the trays 25 and 26, on which the sheet stacks areplaced after being subjected to saddle stitching and center folding,respectively.

Moreover, the stapler pin container of the stapling processing unit 20is disposed below the center-folded-stack tray 26 and thecenter-folded-stack tray 26 is configured to be at least partiallyopenable and closable as illustrated by a dashed line in FIG. 1. Thus,the stapler pin container becomes replaceable from the front surface ofthe sheet finishing device 1. Herein, although the center-folded-stacktray 26 is configured to be partially openable and closable, it is alsopossible to configure the center-folded-stack tray 26 to be entirelyopenable and closable.

Meanwhile, if a stapling position in the stapling processing unit 20 isspaced-apart from a door 6 disposed at the front surface of the sheetfinishing device 1 by a distance L1 that is almost half of the maximumsheet length that can be subjected to finishing processing, then thedoor 6 at the front surface need not be opened even in the case ofperforming saddle stitching of the maximum sheet size that can besubjected to finishing processing.

Similarly, if a nip position of the center-folded-sheet dischargingrollers 33 is spaced-apart from the door 6 of the sheet finishing device1 by a distance L2 that is equal to or more than half of the maximumsheet length, then a saddle-stitched sheet stack or a folded sheet stackcan be stacked on the center-folded-stack tray 26 while keeping the door6 closed.

Moreover, it is possible to perform center folding if the rear end fence14 in the aligning unit 10 is spaced-apart from the folding position bya distance L3 that is at least half of the maximum sheet length.Besides, by keeping the distance L3, the size (longitudinal dimensions)of the sheet finishing device 1 can also be reduced.

FIG. 2 is an explanatory diagram for explaining an overall configurationof an image forming system according to a second embodiment of thepresent invention. In the image forming system shown in FIG. 2, afolding unit is disposed inside the sheet finishing device 1.

In the sheet finishing device 1 illustrated in FIG. 2, a folding unit 50is disposed on the upstream side of the aligning unit 10 (in mid-courseof the feed path 4). If a paper sheet discharged from the image formingapparatus 100 is not to be folded, then that paper sheet is conveyed tothe aligning unit 10; and if a paper sheet discharged from the imageforming apparatus 100 is to be folded, then that paper sheet is guidedinto the folding unit 50.

In the case when the folding unit 50 performs Z-folding, it conveys theZ-folded paper sheet to the aligning unit 10 that then aligns the papersheet. Subsequently, the stapling processing unit 20 performs edgestapling and discharges the paper sheet to the edge-stapled-stack tray25.

In the case when the folding unit 50 performs folding other thanZ-folding, it conveys the folded paper sheet to the aligning unit 10that then aligns the paper sheet. Subsequently, the stapling processingunit 20 performs stapling and discharges the paper sheet to thecenter-folded-stack tray 26.

In this particular configuration, the paper sheet P of a large size(e.g., A3-size) discharged from the lower back portion of the imageforming apparatus 100 to the sheet finishing device 1 is guided by theentry roller pair 3 into the folding unit 50. However, if folding is notrequired, then the paper sheet P is conveyed as it is downward to thealigning unit 10.

To perform edge stapling of A3-size paper sheets after aligning them inA4-size, the A3-size paper sheets need to be Z-folded into A4 size. Forthat, the A3-size paper sheets entering via the entry roller pair 3 areconveyed toward the folding unit 50 by a switching operation of aswitching claw 51. The switching claw 51 is held by a spring (notillustrated) in an orientation that guides a paper sheet toward thealigning unit 10. When a solenoid (not illustrated) is switched ON, theswitching claw 51 rotates and switches to an orientation that guides apaper sheet in the direction toward the folding unit 50. When thesolenoid is kept OFF, the switching claw 51 guides paper sheets in thedownward direction without change.

The folding unit 50 includes a first conveying unit 52, a secondconveying unit 53, a third conveying unit 54, a fourth conveying unit55, an upper end stopper 53 a disposed in the second conveying unit 53,a rear end stopper 54 a disposed in the third conveying unit 54, a firstfolding roller 56, a second folding roller 57, a third folding roller58, a pressure roller 59, and a branching claw 60.

First, depending on the fold size and the fold type, the upper endstopper 53 a and the rear end stopper 54 a are moved by a stepping motor(not illustrated) to predetermined positions inside the second conveyingunit 53 and the third conveying unit 54, respectively. The pressureroller 59 and the first folding roller 56 convey a paper sheet into thesecond conveying unit 53 including the upper end stopper 53 a. Bycontinuing the conveyance even after an end of the paper sheet abutsagainst the upper end stopper 53 a, a slack is formed in the papersheet. The slack eventually gets nipped between the first folding roller56 and the second folding roller 57 so that the paper sheet gets foldedfor the first time. The folded part is then conveyed toward the thirdconveying unit 54 including the rear end stopper 54 a. By continuing theconveyance even after the folded part abuts against the rear end stopper54 a, a slack that is identical to the previous slack is formed in therear portion of the paper sheet. The slack eventually gets nippedbetween the second folding roller 57 and the third folding roller 58 sothat the paper sheet gets folded for the second time. Subsequently, thepaper sheet subjected to Z-folding in the abovementioned manner isguided by the branching claw 60 to the fourth conveying unit 55 and thento the aligning unit 10. Upon being subjected to alignment and edgestapling, the paper sheet gets discharged to the edge-stapled-stack tray25.

In the case of performing outer-three-folding, inner-three-folding,double folding, or quarto folding in the folding unit 50; a paper sheetconveyed from the entry roller pair to the folding unit is then conveyedto a folding section by a switching claw. Then, depending on the sheetsize and the fold type, the upper end stopper 53 a and the rear endstopper 54 a are moved to the respective predetermined positions and thefolding processing is performed in an identical manner to that ofZ-folding. The folded paper sheet is then conveyed by the branching clawtoward the center-folded-stack tray 26. The center-folded-sheetdischarging rollers 33 then discharge the folded paper sheet on thecenter-folded-stack tray 26.

In this way, the folding unit 50 is disposed in the upper part of thespace inside the sheet finishing device 1, the stapling processing unit20 is disposed in the lower part of the space inside the sheet finishingdevice 1, and the folding processing unit 30 performs center foldingwith upward folding direction. Because of such a configuration, thecenter-folded-stack tray 26, on which center-folded sheet stacks areplaced, can also be used as the stack tray for stacking paper sheetsthat are folded singularly (outer-three-folding, inner-three-folding,double folding, quarto folding, etc.). That enables achieving reductionin the size of the sheet finishing device 1.

FIG. 3 is an explanatory diagram for explaining an overall configurationof an image forming system according to a third embodiment of thepresent invention. The description with reference to FIG. 3 is given toindicate that it is possible to alternately manufacture theconfiguration illustrated in FIG. 2 (including the folding processingunit 30 and the stapling processing unit 20 that is capable of edgestapling and saddle stitching) and the configuration illustrated in FIG.3 (exclusively used as an edge stapling unit).

More particularly, in the configuration illustrated in FIG. 2, thefolding processing unit 30 and the stapling processing unit 20, which iscapable of edge stapling and saddle stitching, are disposed at thebottom surface of the device along the longitudinal direction. However,from the perspective of a user needing to perform only edge stapling,the edge-stapled-stack tray 25 is disposed in a narrow space.Alternatively, the folding processing unit 30 and the staplingprocessing unit 20 are replaced with the large-capacityedge-stapled-stack tray 25 and an edge stapling unit 23 is detachablyattached to the rear end fence 14 of the aligning unit 10, while keepingthe housing and the other constituent elements of the sheet finishingdevice 1 intact. Thus, the configurations illustrated in FIGS. 2 and 3become mutually replaceable so that sheet finishing devices performingonly edge stapling and sheet finishing devices performing edge staplingas well as saddle stitching can be manufactured without difficulty. Thatmakes it possible to meet the user demands in a speedy manner and at alow cost. Meanwhile, if the folding unit 50 is disposed in theconfiguration illustrated in FIG. 3, then it also becomes possible toperform center folding.

In the sheet finishing device 1 illustrated in FIG. 2 that is capable ofperforming edge stapling as well as saddle stitching, the staplingposition is spaced-apart from the door 6 disposed at the front surfaceof the sheet finishing device 1 by a distance smaller than the maximumsheet size. Thus, to enable stacking of an edge-stapled sheet stack onthe edge-stapled-stack tray 25, the door 6 at the front surface needs tobe kept open. Instead, a hole can be formed so that an edge-stapledsheet stack does not make contact with the door 6 or, as illustrated inFIG. 4, a small door 6 a can be disposed that opens when pushed by anedge-stapled sheet stack. Such a configuration enables stacking of sheetstacks while keeping the door 6 at the front surface closed.

In this way, in the present embodiment, since a sheet finishing devicecapable of performing center folding is disposed within the installationarea of an image forming apparatus, it is possible to provide the sheetfinishing device and an image forming system that do not take any extraoccupancy area.

Moreover, in the sheet finishing device disposed beneath the imageforming apparatus, a folding processing unit is disposed on the upstreamside and a stapling processing unit is disposed on the downstream sideso that a space can be secured for housing a stack tray forsaddle-stitched sheet stacks.

Furthermore, by disposing a driver unit that includes a stapler pincontainer and a stapler pin pushing unit below a center-folded-stacktray, the stapler pin container can be replaced by opening thecenter-folded-stack tray from the front surface of the sheet finishingdevice.

Moreover, since a stapling position in a stapling unit is spaced-apartfrom a door at the front surface of the sheet finishing device by adistance that is almost half of the maximum sheet length, it becomespossible to perform saddle stitching without having to open the doordisposed at the front surface of the sheet finishing device.

Furthermore, since the nip position of a discharging roller pair used indischarging a saddle-stitched sheet stack is spaced apart from the doorof the sheet finishing device by a distance equal to or more than halfof the maximum sheet length, it becomes possible to perform saddlestitching without having to open the door disposed at the front surfaceof the sheet finishing device.

Moreover, by discharging folded sheet stacks and saddle-stitched sheetstacks to a common tray, stacking of paper sheets can be performed whilereducing the size of the sheet finishing device.

Furthermore, by replacing the stapling processing unit capable ofperforming edge stapling as well as saddle stitching and the foldingprocessing unit with a large-capacity edge-stapled-stack tray and bydetachably attaching an edge stapling unit to an aligning unit, the twodifferent configurations become mutually replaceable so that sheetfinishing devices performing only edge stapling and sheet finishingdevices performing edge stapling as well as saddle stitching can bemanufactured without difficulty. That makes it possible to meet the userdemands in a speedy manner and at a low cost.

Moreover, if a folding unit and the stapling processing unit areintegrated into a detachable configuration and if a stapling processingunit is made detachably attachable at an end of the aligning unit; then,in the case of a dedicated edge stapling device, the folding unit andthe stapling processing unit is removed and a stapler for edge staplingis newly disposed so that the cost can be reduced and a sheet stack ofthe maximum size can be stacked inside the device at the time ofstapling.

Furthermore, the conveying rollers that convey a sheet stack to thestapling position are disposed across the conveying path and operate inpair. Thus, by driving both the conveying rollers, the horizontalconveyance of the sheet stack can be performed with less misalignment inthe paper sheets.

Moreover, since the folding processing unit disposed on the upstreamside of the stapling processing unit folds a sheet stack in thesubstantially central part, it is possible to configure a sheetfinishing device that performs center folding in the center of saddlestitching.

Furthermore, since the rear end fence in the aligning unit isspaced-apart from the folding position by a distance that is half of themaximum sheet length, it becomes possible to minimize the depth of thesheet finishing device.

Moreover, at a saddle-stitched-sheet discharging location on the door atthe front surface of the sheet finishing device, a hole can be formed toavoid hindrance in sheet stack conveyance or a small door can bedisposed that opens when pushed by the sheet stack from inside. Becauseof that, even if edge stapling of a sheet stack of the maximum length isperformed, the sheet stack can be discharged without having to open thedoor at the front surface.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. An image forming system comprising: an image forming apparatus thatforms an image on a paper sheet; and a sheet finishing device thatperforms finishing of a paper sheet discharged from the image formingapparatus, wherein the sheet finishing device includes an aligning unitthat stacks and aligns a plurality of paper sheets on an alignment traythereby forming a sheet stack, and a stapling processing unit thatperforms stapling with respect to the sheet stack, and the sheetfinishing device is disposed beneath the image forming apparatus.
 2. Theimage forming system according to claim 1, wherein the staplingprocessing unit includes an edge stapling unit that subjects the sheetstack to edge stapling by stapling an edge of the sheet stack, and asaddle stitching unit that subjects the sheet stack to saddle stitchingby stapling a central part of the sheet stack, and the sheet finishingdevice includes a center folding processing unit that subjects the sheetstack to center folding by folding, in center along a sheet conveyingdirection, the sheet stack subjected to the saddle stitching at thesaddle stitching unit, a first discharging tray that houses the sheetstack subjected to the edge stapling at the edge stapling unit, and asecond discharging tray that houses the sheet stack subjected to thecenter folding at the center folding processing unit.
 3. The imageforming system according to claim 2, wherein the center foldingprocessing unit includes a configuration to fold a central part of asheet stack held horizontally in upward direction, the staplingprocessing unit includes a driver unit including a detachable staplerpin container containing a stapler pin and a stapler pin pushing unit,and a clincher unit that folds a tip of the stapler pin, and the driverunit is disposed beneath the second discharging tray and is configuredin such a way that, by opening and closing the second discharging trayentirely or partially, the staple pin container is replaceable.
 4. Theimage forming system according to claim 1, wherein a stapling positionin the stapling processing unit is spaced-apart from a door disposed ata front surface of the sheet finishing device by a distance that isabout half of a maximum sheet length.
 5. The image forming systemaccording to claim 2, wherein a nip portion of a pair ofcenter-folded-sheet discharging rollers that guide the sheet stacksubjected to saddle stitching to the second discharging tray isspaced-apart from a door disposed at a front surface of the sheetfinishing device by a distance substantially equal to or more than halfof a maximum sheet length.
 6. The image forming system according toclaim 2, wherein a folding unit is disposed on an upstream side of thealigning unit in such a way that, when a paper sheet discharged from theimage forming apparatus is not to be folded, the paper sheet is conveyedto the aligning unit and, when the paper sheet is to be folded, thepaper sheet is guided into the folding unit, when the folding unitperforms Z-folding, a paper sheet subjected to Z-folding is conveyed tothe aligning unit that aligns the paper sheet after which the staplingprocessing unit performs edge stapling and discharges the paper sheet tothe first discharging tray, and when the folding unit performs foldingother than Z-folding, a paper sheet subjected to folding is conveyed tothe aligning unit that aligns the paper sheet after which the staplingprocessing unit performs stapling and discharges the paper sheet to thesecond discharging tray.
 7. The image forming system according to claim2, wherein the center folding processing unit and the staplingprocessing unit are replaceable with a large-capacity edge-stapled-stacktray, and an edge stapling unit is detachably attached to the aligningunit.
 8. The image forming system according to claim 1, furthercomprising a pair of conveying rollers that are disposed across aconveying path for conveying the sheet stack aligned by the aligningunit to the stapling processing unit, wherein each of the pair ofconveying rollers is a driving roller.
 9. The image forming systemaccording to claim 2, wherein the aligning unit includes a sheet rearend fence that determines a position of a rear end of a paper sheet, andthe sheet rear end fence is spaced-apart from a folding position in thecenter folding processing unit by a distance that is about half of amaximum sheet length.
 10. The image forming system according to claim 1,further comprising an edge-stapled-sheet discharging unit includingeither one of a hole that ensures that conveyance of a sheet stack isnot hindered by a door disposed at a front surface of the sheetfinishing device and a door that is openable when pushed by a sheetstack from inside.